Chemical polishing machine



Aug. 31, 1965 K` F. KlPP ETAL 3,203,434

CHEMICAL POLISHING MACHINE Filed Dec. 6, 1965 4 Sheets-Sheet 1 Aug 31, 1965 K. F. KlPP ETAL 3,203,434

CHEMICAL POLISHING MACHINE Filed Deo. 6, 1965 4 Sheets-Shea?l 2,

Aug. 31, 1965 K. F. KlPP ETAL CHEMICAL POLISHING MACHINE 4 Sheets-Sheet 5 Filed Deo. 6, 1963 H Illllm [lllll-I Il HLM l Aug. 31, 1.965

Filed DeC. 6. 1963 K` F. KIPP ETAL CHEMICAL POLISHIG MACHINE 4 Sheets-Sheet 4 United States Patent 3,203,434 CHEMICAL FULESHING MACHHNE Karl F. Kipp, Nazareth, and .loseph A. Santangini, Bethlehem, Pa., assigner-s to Western Electric Company, ln-

corporated, New York, N.Y., a corporation of New York Filed Dec. 6, 1963, Ser. No. 328,6l2 6 Claims. (Cl. 134-57) This invention relates to a chemical polishing machine, and more particularly to a planetary geared machine for rotating silicon slices `about a pair of axis in an etchant solution and then in a rinse solution.

In the manufacture of transistors, small slices of semiconductor material are used as active elements. These slices, or discs, consist -of a base slice of material; such as, silicon having a first predetermined resistivity characteristic, and onto which is deposited, from a gas such as silicon tetrachloride, a thin layer of silicon having a second predetermined resistivity characteristic. One of the problems in the manufacture of such transistors resides in the necessity of having the base silicon slice provided with a smooth, undamaged surface onto which the silicon layer is deposited. The silicon slices are usually cut from a cylindrical crystal stock, mechanically lapped and polished, and finally subjected to an etching process to remove yany residual damage that appears on the surface of the slices.

The chemical etching, or polishing, must be accomplished by moving the slices in an etchant solution. During the movement of the slices through the etchant, care must be taken to avoid feathering of the edges of the crystal slices and the formation of ridges or waves on the crystal surface resulting from the passage of the slices through the etchant solution.

An object of the invention is to provide a new and improved polishing machine.

Another object of the invention resides in a polishing machine for rotating silicon slices in an etchant solution while simultaneously agitating the solution to effectuate a uniform etch of the silicon slices.

A further object of the invention resides in a planetary gearing arrangement for selectively rotating silicon slices in either an etchant tank, or in a rinse tank.

An additional object of the invention is the provision of a novel fixture for holding and rotating tiers of silicon slices in a solution while permitting the slices to rotate about their own centers to insure an exposure of all critical surfaces to a uniform etching action.

A still further object of the invention resides in automatic means for transferring a silicon slice holding tixture from an etchant solution in response to a predetermined rise in temperature of the solution which rise is indicative of a predetermined etching action.

With these and other objects in view, the present invention contemplates a chemical polishing machine having a plurality of holders or fixtures for silicon slices and facilities for moving the holders in an agitated etchant solution. The holders are rotated by a planetary gearing arrangement which also functions to rotate paddles to agitate the etchant solution. In addition, facilities are provided to automatically move the holders, and the paddles from the etchant solution into a rinse solution whereaft-er the lplanetary gearing arrangement is again operate-d to rotate the holders and paddles in the rinse solution.

Other objects and advantages of the present invention will be apparent from the following detailed description when considered in conjunction with the accompanying drawings:

FIG. 1 is a top view of a chemical polishing machine ICC having silicon slice holding fixtures that may be selectively moved from an etchant tank to a rinse tank.

FlG. 2 is a side elevation view of the chemical polishing machine shown in FIG. 1 particularly illustrating the facilities for moving the slice holding fixtures from one tank to the other.

FIG. 3 is a top view of the slice holding fixtures and a drive mechanism for rotating slice holders and agitator paddles.

FIG. 4 is a sectional view taken along line 4-3 of FEC'. 3 particularly depicting the structure of slice holding fixtures and the planetary gear mechanism for driving both the slice holding fixture and the agitator paddles.

FIG. 5 is a sectional view taken along line 5*-5 of FIG. 5 showing the construction of an individual slice holder.

FIG. 6 is a sectional view taken along line 6 6 of FlG. 5 showing a silicon slice on a mount positioned within a recess formed in the holder.

FIG. 7 is a side view of an alternative embodiment of the invention showing a combined slice holder and paddle agitator.

FlG. 8 is a sectional view taken along line 8 8 of FIG. 7 showing the alternative holder and three recesses for receiving mounted slices, and

FIG. 9 is a schematic circuit diagram showing facilities for automatically moving the fixture from one tank to the other. Y

Referring first to FIGS. 5 and 6, there is shown a silicon slice or disc lll) adhered by a suitable cement or wax t0 a cylindrical projection lia of a slice mount 11 constructed of tetrafluoroethylene. The machine shown in the other figures is designed to rotate the slice lt) in an etchant solution and then in a rinse tank.

Referring now to FIGS. l and 2, there is shown a housing Il?. having a top i3 that provides a support for a pair of tanks le and liti extending into the housing. The tank lll contains an etchant solution which may comprise five parts nitric acid, one part of hydrochloric acid, and 4.4 parts of acetic acid saturated with iodine crystals. The tank lo contains a suitable rinse solution for removing the etchant solution adhering to the slices It) following the etching application.

Secured to the top 13 is a vertical extending post, or standard 1'7, having a pair of parallel trackways 1li and 19 terminating in a cross-over trackway section 2l. Mounted about the post i7 is a hub 23 having apin or rider 24 positioned to move within the traclcways 18 and 19. Laterally extending from the hub 23 is a support bracket, or arm 25 lattached to a cover 26. Cover 26 is provided with three guide collars 28 to receive guide rods 29, or guide rods 3l, positioned respectively about the tanks i4 and le. The cover 26 provides a mounting for a motor 32 which supplies the motive means for agitating the solutions contained in the tanks 14 and 16, as well as means for imparting movement to the slices lt) positioned within the tanks le and 16.

Referring now to FIGS. 3 and 4, the motor 32 on the cover 26 drives a bevelled gearing arrangement 33 and a shaft 34. This shaft 34 extends through a bearing assembly 36 and the cover 26 to provide a support for a carrier plate 37. Depending from the carrier plate 37 are four fixtures generally designated 38 for supporting the mounted slices lll. Each fixture includes a plurality of individual holders 39 secured to and spaced along support rods dl. The tops of the support rods 41 are attached to a plate 42 mounted on a shaft 43 extending through the carrier plate 37. A pair of collars 46 and 47 are secured to each shaft 43 and thus provide bearing supports for each fixture 38.

The facilities for rotating the fixtures 38 in the tanks 3 14 and 16 includes a planetary gearing arrangement comprising four planet gears 50 secured to the upper ends of the shafts 43. Secured to the underside of the cover plate 46 is a spacer 51 providing a fixed mounting for a sun gear 52. It will be noted that the shaft 34 extends through the fixed sun gear 52 into a hub 53 fixed to the carrier 37. Rotation of the motor 32 is thus imparted through the shaft 34 to the carrier plate 37 to rotate the planet gears 50 about the stationary sun gear 52. As the planet gears t) orbit about the sun gear 52, each planet gear is rotated about its own center.

Attention is directed to FIG. 5 wherein one of the holders 39 is shown as being provided with three cutout sections 56. These cutout sections are provided to allow an attending operator to readily load and unload the mounts 11 into a recess 57 formed in the holder 39. Inasmuch as each mount 11 is constructed of tetraflouroethylene, a low friction material, the mount can rotate within the recess 57.

Returning now to a further consideration of FIGS. 3 and 4, there is shown a plurality of shafts 58 provided with radiating paddles 59. The shafts 58 extend through suitable apertures formed in the carrier 37 and are rotatably mounted on the carrier by means of bearing collars 61 and 62. Attached to the upper end of each shaft 58 is a pinion 63 that meshes with the sun gear 52. As the carrier 37 is rotated, the pinions 63 react with the stationary sun gear 52 to rotate the shafts 58 and the paddles 59, thereby imparting a turbulence to either the etchant solution in the tank 14, or the rinse solution in the tank 16.

The etching action is monitored by a thermocouple 64. It has been found that the extent of etching is proportional to the rise in temperature of the etchant solution. When the thermocouple 64 detects a predetermined rise in temperature, a suitable meter may be actuated to indicate to the attending operator that the etching operation has been completed to remove a predetermined amount of material from the slice 10.

Considering now the facilities for automatically transferring the fixtures 38 from one tank to another and referring again to FIGS. 1 and 2, there is shown secured to hub 23 a splined sector or gear 64 meshing with a rack 66 actuated by an air cylinder 67 and piston 68. When the fixtures 38 are elevated so that the rider 24 of the hub 23 is located in the crossover trackway section 21, the air cylinder may be selectively operated to shift the cover 26 and fixtures 38 over either the etchant tank 14 or the rinse tank 16.

When the air cylinder 67 is operated to shift the fixtures 38 over the tank 14, a hole, or opening 69, in the support bracket rides over and onto a laterally projecting section 70 of an elevator rod 71 which is attached to a piston contained within an air cylinder 72. The rider 24 is now positioned to ride in vertical trackway 18. Subsequent operation of air cylinder 72 lowers the elevator rod 71 to move the fixtures 38 within the tank 14. As the fixtures 38 move into the tank 14, the guide rods 29 pass through the guide bearings 28 to position the fixtures 38 within the tank 14. The motor 32 is operated to rotate the carrier plate 37; wereupon, the gears 50 and 63 rotate the fixtures 38 and the paddles 59. The individual mounts, with the slices 10, are thus rotated about both the axis of the shafts 34 and the individual axis of the shafts 43. Due to the low friction characteristics of mounts 11, these mounts are free to further move within the recess 57. The planetary movement of the mounts 11 insures that the leading edge of the slices 10 continuously changes to thus prevent feathering of the slices 10.

Upon the thermocouple 64 ascertaining a predetermined temperature rise, indicative of a completion of the etching operation, the air cylinder 72 is operated to raise the elevator rod 71 to lift the fixtures 38 from the tank and again position the rider 24 in alignment with the crossover trackway section 21. The air cylinder 67 is again operated to move the rack 66 toward the right to swing the hub 23, support bracket 25, and attached fixtures 38 in a counterclockwise direction, thereby positioning the fixtures 38 over the tank 16 and the rider 24 in alignment with the vertical trackway 19. As the support bracket 25 swings, the hole 69 moves over and onto a laterally projecting section 73 of an elevator rod 74 which is attached to a piston within an air cylinder 76. Subsequent operation of the air cylinder 76 lowers the elevator rod 74 to move the fixtures 38 into the tank 16. The motor 32 is again operated to orbit and rotate the slices 10 through the rinse solution which is agitated by the movement of the paddles 59. After a suitable time delay the air cylinders 76 and 67 are se'- quentially operated to lift the fixtures 38 from the tank 16 and swing the support bracket 25 so that the rider 24 is positioned at the mid-point of the crossover trackway section 21. The attending operator may now unload the etched slices 10 from the fixtures 38 and load unetched slices 10 in anticipation of another cycle of operation.

Attention is directed to FIG. 9 which discloses a control circuit for automatically moving the fixtures 38 from a load position, to the etch tank 14, to the rinse tank 16 and then to an unload position. Assume that both elevator rods 71 and 74 are in the raised position, that the rider 24 is at the midpoint of the crossover trackway section 21, and that the operator has loaded the fixtures 38 with mounts 11 having slices 10 cemented thereto, the operator first depresses a start button 81 to complete an energizing circuit for relay 82 which draws up contact 82a to complete a locking circuit through normally closed contact 84a of a switch 84. This switch 84 (see FIG. 1) is mounted on the elevator rod 71 and is operated by engagement with the support bracket 2S. Energization of relay 82 also closes contact 821; to complete an energizing circuit for a solenoid 87 which controls the application of air to cylinder 67, whereupon the piston rod 68 and rack 66 are moved to the left thus rotating the splined gear sector 64 and swinging the support bracket 25 into engagement with the switch 84. Contacts 84a of switch 84 are opened to release the locking circuit for relay 82, which in turn releases contact 82h to deenergize solenoid 87.

As switch 84 is engaged by bracket 25, contact 84h is closed to complete an energizing circuit through normally closed contact 88a of a switch 88 and through a solenoid 89 that controls the application of air to cylinder 72. Switch 88 (see FIG. 2) is mounted on the housing top 13 and in position to be engaged by the descending cover 26. When the support bracket 25 swings to the left the lateral projecting section 7l) of the rod 71 engages and supports the bracket within the hole 69. Application of air to cylinder 72 lowers the rod 71 to move the fixtures 38 into the tank 14 and to move the cover 26 into engagement with switch 88. Contact 88a thereupon opens to deenergize solenoid 89 and a contact 8812 is closed to complete an energizing circuit for the motor 32.

The motor 32 will function to rotate the fixtures 38 and the paddles 59 until the thermocouple 64 ascertains a predetermined temperature rise, indicative of the completion of a predetermined etching action, whereupon the thermocouple through suitable well-known commercial controls closes a switch 91 to complete an energizing circuit through normally closed contact 92a of a deenergized relay 92, through the now closed thermocouple switch 91, and through a solenoid 94. Energization of solenoid 94 effectuates the application of air to the cylinder 72 to return the elevator rod 71 to the up position and thus move the fixtures 38 from the tank 14. Closure of ther' mocouple switch 91 also completes an energizing circuit for a relay 96 which draws up contact 96a to complete a locking circuit for the solenoid 94. Therefore, as the fixtures 38 are withdrawn from the tank 14, the thermocouple relinquishes control of the energization of the solenoid 94, but the fixtures are insured of being lifted to the up position because of a locking circuit now estabiished through Contact 96a to the solenoid 94. Also, as the cover 26 moves from engagement with the switch 8S, the contact 88h is opened to interrupt operation of the motor 32.

When the cover 26 reaches the up position, a switch 98 is engaged and operated to close a contact 98a and complete a circuit through now closed contact 96b of energized relay 96, through now closed contact 98a and through a solenoid 101. Solenoid 101 is effective to control the application of air to cylinder 67 which drives piston rod 68 and rack 66 toward the right to thus rotate spline gear 64 and support bracket 25 in a counterclockwise direction to advance the hole 69 over the lateral projection 73 of the rod 74. The lateral projection 73 passes through the hole 69 to engage and support the bracket 25. When the contact 98a closes, a circuit is also completed through the relay 92. The relay 92 opens contact 92a to interrupt and return to the initial condition the circuits to the solenoid 94 and the relay 96. Relay 92 draws up a contact 92h to complete a locking circuit through a contact 103m of a switch 103 to both the relay 92 and the solenoid 101. Switch 103 is mounted on elevator rod 74 (see FIG. 1) and is operated by the counterclockwise swinging bracket 25.

Operation of switch 103 also effectuates a closing of contact 1031; to complete a circuit through normally closed contact 104er of a switch 104 (see FIG. l) and through a solenoid 106. Solenoid 106 controls the application of air to the cylinder 76 which functions to lower the elevator rod 74 and move the fixtures 3d and paddles 59 into the tank 16. As the elevator rod '74 descends, the cover 26 engages and operates the switch 104 which opens contact 104a to interrupt the circuit for the solenoid 106. Operation of switch 104 also effectuates a closure of a Contact 10417 to complete an energizing circuit to a motor driven timer 107. Timer 107 is of a well known commercial type that functions to close contacts after a predetermined time delay, Closure of contact 10419 also completes a circuit through normally closed Contact 108er of a deenergized relay 108 to the motor 32, which functions to rotate the fixtures 3S and paddles 59 in the rinse solution contained in tank 16.

After a predetermined time, suiiicient to thoroughly rinse the etched slices 10, timer 107 is effective to close contacts 10751 and 10721 to complete a holding circuit for the timer and to complete an energizing circuit for the relay 103 which opens contact 101311 to interrupt the circuit for the motor 32. Closure of timer contact 107e is also effective to complete a circuit through normally closed contact 109e of a switch 109 (see FIG. 1) to a solenoid 111. This solenoid 111 is effective to control the application of air to the cylinder 76 to return the elevator rod 74 to the up position. The fixtures 33 and cover 26 are thus moved up and the cover engages and operates the switch 109. When switch 109 operates, contact is opened to deenergize solenoid 111 and contact 10% is closed to complete an energizing circuit through now closed contact 1031 of energized relay 10? and through now closed contact 1091) to relay 112. Energized relay 112 draws up Contact 112e to complete a circuit through a normally closed Contact 113a of a switch 113 (see FIG. 1) to solenoid 87 which functions to supply air to the cylinder 67. The application of air to cylinder 67 moves the piston rod 68 and the rack 66 toward the left and the splined gear 64 and support bracket 25 are rotated in a clockwise position until switch 113 (see FIG. l) is engaged and operated. During this movement the rider 24 moves along the crossover trackway section 21 to support fixtures 3S above the housing top 13. Operation of switch 113 opens the normally 6 closed contact 113a to interrupt the circuit for solenoid 37 whereupon the movement of the rack 66 and pivoting of the bracket 25 are halted to position the fixtures 33 above the housing top 13 and midway between the tanks 14 and 16.

A contact 113b of switch 113 is also opened to deenergize the timer 107 to release its contacts 107a and 1071) and to deenergize the relays 10S and 112. The circuit is now restored to the initial condition and the attending operator unloads the etched slices 10 and reloads the fixtures 38 with unetched slices in preparation for another cycle of operation.

All cooperating parts that are exposed to the etchant solution; such as, the tank 14, the fixtures 38, the paddles 39, and the associated gearing and support structure are constructed of polyvinylchloride, or other suitable material, which is not attacked by the etching solution.

Referring now to FIGS. 7 and 8, there is shown an alternate fixture that can be used with the drive mechanism shown in association with the embodiment disclosed in FIGS. l to 6. More particularly, this alternative embodiment comprises a shaft 116 connected to an internally threaded knurled collar 117. The internal threads of collar 117 engage threads formed on a sleeve 113. Extending from the sleeve 11S is a stud shaft 119 that provides a mounting for a hub 121 formed on a planet gear 122 similar in construction to the planet gear 't. The knurled collar 117 and sleeve 11S provide a chuck to permit the quick detachment of the shaft 116 following a chemical polishing operation. Attached along the shaft 116 are a number of holders 123, each of which include radiating sections 126, 127, and 128, each having a recess 129. The recesses 129 are adapted to receive three mounts 11 having slices 10 fermented thereto. Radiating from each holder 123 is a paddle 131, which when rotated imparts a turbulence to either the etchant or the rinse solution.

In use of the fixture constituting the alternative of the embodiment of the invention shown in FlGS. 7 and 8, the attending operator will load the mounts 11 into the recesses 129 and then lower the fixtures 123 into the tank 14. The movement of the fixtures can be effected by manually moving the support bracket 2S and rider 24 along the guideways 18, 1f, and 21, shown in FG. l, or by operation of the automatic facilities described in relation to the first embodiment. The motor 32 drives the carrier 37 to rotate planet gears 122 about the stationary sun gear S2. The planet gears 122 are thus rotated about their own axis to rotate the shaft 116 and the slice holders 123 and the paddles 131. As the holders 123 rotate about the shaft 116, the lead edge of each slice 111 is moved with respect to the path of rotation about sun gear S2. This continuing shifting of the lead edge of the slice 10 prevents any portion `of the slices from being exposed to a greater etching action than any other portion. The orbiting and rotation of the slices 10 prevent feathering of the edges and the formation of ridges on the exposed surfaces yof the slices 10.

lt is to be understood that the above-described arrangements of apparatus and construction of elemental parts are simply illustrative of an application of the principles of the invention and many other modifications may be made without departing from the invention.

What is claimed is:

1. ln an apparatus for etching the surface of a silicon disc that is attached to a circular support,

a tank for receiving an etchant solution,

a cover for said tank,

a stationary gear mounted on the underside of said cover and within said tank above the level of the solution,

a rst Vertical shaft extending through said cover and said gear,

a carrier plate mounted on the lower end of said first shaft,

a first planet gear rotatably mounted on said carrier plate and meshing with said stationary gear,

a holder attached to said planet gear and depending into the solution,

said holder having a horizontally extending circular recess to receive said circular support to allow said circular support to rotate within said recess,

a second planet gear rotatably mounted on said carrier plate and meshing with said Stationary gear,

a second shaft means depending vertically from said second planet gear and having a plurality of radially extending paddles, and

means for rotating said first shaft to rotate said planet gears about said stationary gear to rotate said support and said second shaft means and paddles.

2. In a chemical polishing machine,

a housing,

a pair of spaced tanks mounted in said housing for receiving an etchant solution and a rinse solution, respectively,

a carrier plate,

a part holder rotatably mounted on and extending from said carrier plate,

an agitator rotatably mounted on and extending from said carrier plate in parallel relationship to said part holder,

a planetary gear mechanism mounted on said carrier plate for orbiting said holder and agitator in a circular path and rotating said holder and agitator with respect to each other,

an arm means connected at one end to said carrier plate and provided with a hub at the opposite end,

a post mounted on said housing and projecting through said hub to support said carrier plate,

said post having a pair of parallel vertical trackways terminating in a cross-over trackway section interconnecting said parallel trackways,

a rider projecting from said hub into said trackways to selectively position said carrier plate over said tanks to position said holder and agitator in one 'or the other of said tanks, and

said cross-over trackway having a straight section for receiving the rider to hold the carrier plate in an elevated position.

3. In a chemical polishing machine for a silicon slice,

a tank for receiving an etchant solution that reacts with silicon and rises in temperature in accordance with the extent of etching of the silicon,

means for supporting a silicon slice in said tank,

normally unoperated means for moving the supporting means to withdraw the slice from the tank, and

means responsive to a predetermined temperature rise in the etchant solution for operating said moving means to withdraw the supporting means and slice from the tank.

4. In a machine for chemically polishing a slice of silicon,

S means from a position with the holding means in said first tank to a position with said holding means in said second tank,

means responsive to a predetermined temperature rise in said etchant solution for operating said transferring means, and

means operated by the transferring means positioning said holding means in said second tank for operating said selectively operable means to rotate and orbit said holding means in said rinse solution.

5. In an automatic chemical polishing machine for silicon slices,

a first tank containing an etchant solution that rises in temperature in response to an etching of silicon,

l5 a second tank containing a rinse solution,

a carrier including a plurality of silicon slice holders mounted for rotational and Orbital movement,

means for moving the carrier to advance the holders into the first tank and submerge the silicon slices in the ctchant solution,

drive means responsive to said advance of the carrier for rotating and orbiting the holders within said rst tank,

means responsive to a predetermined rise in temperature of the etchant solution for interrupting said drive means and for moving the carrier to remove the holders from within the rst tank,

transfer means responsive to the removal of the carrier for advancing the carrier to move the holders into the second tank,

means responsive to the advance of the carrier by the transfer means for again actuating the drive means, and

a timer means actuated after a predetermined delay for moving the carrier to remove the holders from the second tank.

6. In an apparatus for etching the surface of a silicon disc,

a circular mount having a cylindrical projection for mounting said silicon disc,

said cylindrical projection having a diameter smaller than the diameter of said silicon disc,

a tank for receiving an etchant solution,

a plurality of vertical supporting rods spaced about a center and extending into said tank,

a horizontal plate mounted on and between said supporting rods having a circular recess formed about said center for receiving and supporting the base of said circular mount to rotate about its own axis,

said recess having a depth sufficient to position said cylindrical projection and silicon disc above the surface of said horizontal plate,

a shaft parallel to said supporting rods and spaced therefrom,

a paddle mounted on said shaft juxtaposed to said plate,

means for orbiting said supporting rods and said shaft in a circular path through said etchant solution, and

means for rotating said supporting rods about said center to rotate said horizontal plate, and simultaneously rotating said shaft to rotate said paddle relative to said plate.

Tiefer-ences Cited by the Examiner UNITED STATES PATENTS 1/23 Reatherford 134-142 1/38 Friedman 134-77 5/44 Keelinel 134-77 X 6/50 Schurenberg 134-77 7() CHARLES A. WILLMUTH, Primary Examiner.

GEORGE I. NORTH, Examiner. 

3. IN A CHEMICAL POLISHING MACHINE FOR A SILICON SLICE, A TANK FOR RECEIVING AN ETCHANT SOLUTION THAT REACTS WITH SILICON AND RISES IN TEMPERATURE IN ACCORDANCE WITH THE EXTEND OF ETCHING OF THE SILICON, MEANS FOR SUPPORTING A SILICON SLICE IN SAID TANK, NORMALLY UNOPERATED MEANS FOR MOVING THE SUPPORTING MEANS TO WITHDRAW THE SLICE FROM THE TANK, AND MEANS RESPONSIVE TO A PREDETERMINED TEMPERATURE RISE IN THE ETCHANT SOLUTION FOR OPEATING SAID MOVING MEANS TO WITHDRAW THE SUPPORTING MEANS AND SLICE FROM THE TANK. 